The Best Time Of Year To Use Pre-Emergent On Your Lawn (And How To Apply It)

Unless you've joined a very small club of people who enjoy turfgrass interspersed with dandelions, henbit, clover, and other interlopers, applying a pre-emergent herbicide to your lawn is one of the most effective things you can do to kill weeds like henbit (whether you know their names or not). But when is the best time to do it?

To get clarity, Hunker spoke exclusively with Lawn Squad, Franchise Training Coordinator & Business Coach Ryan Walts about when and how to use pre-emergents most effectively. He emphasized how useful pre-emergents can be. "Their primary benefit is stopping weed seeds from ever sprouting," he said, "which means less time spent pulling or spraying weeds later on." And it's not just about having a uniform lawn, Walts said, but about eliminating competition for nutrients, water, and light. Weeds will happily consume these resources and, in the process, just as happily deprive your hard-earned grass of them.

Now, as for the "when" question? Because pre-emergents do their work before weeds emerge, early spring is the ideal time to apply them. But Walts also cautions that you shouldn't foil your own efforts by stifling new grass growth. "It's important to remember pre-emergents can also inhibit the growth of new grass seed," he said. "If you're planning to overseed or repair your lawn at the same time you apply pre-emergent, avoid using pre-emergent in those areas to allow the grass seed to establish properly."

While an early spring application of pre-emergent herbicides is a great step toward weed control, it's not all you can do, and it's not the only time you can do it. When Hunker spoke exclusively with Lawn Squad's Ryan Walts, he explained that using pre-emergent early in the growing season will, indeed, keep crabgrass and other weeds from germinating, and that you should also take the opportunity to feed your lawn. "For added effectiveness," Walts said, "pair pre-emergent with fertilizer. This will give the grass a boost while creating a protective barrier against weeds."

If you miss that early spring window, all is not lost. "If you miss the early spring application, you still have options. A second effective window is in late summer to early fall," Walts said. "Similarly, apply before soil temperatures drop below 70 degrees but are still higher than 55 degrees." A fall application of pre-emergent isn't your best bet, but it's worth it. "This can still significantly reduce weed pressure heading into the next growing season," he said.

The "pre" in "pre-emergent," of course, implies that there's also a wrong time to use it for weed control. "The least effective time to apply pre-emergent is after weeds have already germinated and broken through the soil's surface," Walts said. Once weeds have begun to sprout – usually in late spring or summer – it's time to turn to post-emergent treatments, since pre-emergents will be less effective for the current growing season. "While it's never 'too late' to take action against weeds, using the wrong product at the wrong time reduces its effectiveness," Walts said.

The effectiveness of your pre-emergent herbicide in controlling common lawn weeds also relies on your ability to use it well. Think about it: The stakes are much higher for the weeds than they are for you, so they'll do whatever they can to survive and prosper. When Hunker spoke exclusively with lawn care expert Ryan Walts, he walked us through the way to ensure you get the most out of your efforts. The best process, as we have seen already, starts with good timing. There's a best time of day to apply most weed-killers, and for pre-emergent, that time is tied to temperature.  "Apply premergentts before soil temperatures reach 55 degrees and are consistently in the 60s throughout the week," Walts said.

To get started, grab a spreader, a garden hose, and the manufacturer's directions. "Spread the product evenly over your lawn using a spreader, then water thoroughly," Walts said. "This activates the pre-emergent and forms a barrier in the top layer of soil." An adequate and even application of activated pre-emergent if the only way to ensure it can do its job. "As weed seeds begin to germinate," Walts explained, "the emerging roots absorb the chemical, preventing growth and ultimately killing the weed."

But don't get carried away, and don't overthink it. You're creating a somewhat durable chemical barrier against weed germination, but trying to help too much can actually interfere. "For best results, avoid disturbing the soil too much after application," Walts said, "as this can break the barrier and reduce effectiveness."